Ash generation of volcanic lapilli during rotary tumbling

Data supporting the publication Hornby, AJ, Kueppers U, Maurer BM, Poetsch C and Dingwell DB (2020) "Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows". In this study, fine ash is generated from lapilli-sized volcanic pumice and scoria in rotary tumbler experiments. We seek to explore ash production processes and clast attrition in natural PDCs, and gain insight into the controlling parameters for particle production efficiency with PDC transport distance. We vary the starting mass, apparatus size, and material properties and tumble clasts over multiple transport distance steps from 0.2-6 km. The data are provided in ASCII or image formats as one zipped folder (2020-025_Hornby-et-al_data.zip) and organised in the following sub-folder structure (for more information please consult the associated data description and Hornby et al (2020): (1) Experimental methods, apparatus and data collections (2) Ash generation data for tumbling experiments (3) Laser particle size distribution data for ash generated in tumbling experiments (4) Post-experimental lapilli size (generated via 3-axis caliper measurements), mass, bulk density and dense rock equivalent (DRE) porosity results (5) 2D image analysis morphology results (6) 2D image analysis size results (7) Cropped, scaled and thresholded images lapilli used for morphometric analysis (8) Image analysis macros and workflow for ImageJ (9) Integrated analysis of results This project has received funding from the European Union's Horizon 2020 research and innovation programme.

In each experiment we collected the following data at each distance step: - Mass of ash produced (<2 mm diameter); - Grain size distribution of produced ash; - Clast morphometrics (via photographs and image analysis) and average mass We ran two sets of experiments (Type I and II) under identical starting conditions. In Type I experiments we returned ash and clasts to the drum, while in Type II experiments we stored the ash and returned only clasts to the drum after every distance step. Further details of the methodology and the apparatuses can be found in the “Methods and materials” file. We also collected 3-axis volume, mass and density measurements of post-experimental clasts for a subset of experiments. We use the median values for material properties to characterise the different samples (two pumice samples and one scoria sample) and to analyse the results. We calculate the ash production rate and estimate the average change in clast size and bedload volume at each tumbling distance. We use clast and bedload dimensions to scale our results. We calculate the flow rate and inertial number for each experiment, as well as a set of associated parameters.